Exploring California’s Marine Protected Areas: Submarine Canyon Habitats

Deep and mysterious waters lie just off California’s coast, sometimes within a stone’s throw of the beach. A millennium of tectonic forces, and more recent geologic forces like ice ages and erosion have brought these present-day deep ocean habitats, called submarine canyons, to our coastal doorstep. Exotic ocean life and biological diversity abound in these deep canyons.

Submarine canyons connect the deep and shallow worlds of our coastal ecosystem. Thirty of California’s 124 marine protected areas (MPAs) protect portions of submarine canyons or steep walls deeper than 650 feet. Recently, researchers visited several of these deepwater MPAs to explore and bring back imagery of strange, unique, and rarely seen marine animals, adding to the collective understanding of California’s rich coastal ecosystem.

The seafloor region where canyons occur is known as the continental margin. It forms the boundary between our relatively shallow coast and the expansive abyssal plain of the Pacific Ocean. Submarine canyons cut through the continental shelf and slope, resembling steep mountain valleys extending towards shore.

squat lobster
Squat lobster at Portuguese Ledge SMCA (1,210 feet)

At over a mile deep, California’s Monterey Submarine Canyon rivals the Grand Canyon in depth, and crosses into two state marine conservation areas (SMCAs): Soquel Canyon SMCA and Portuguese Ledge SMCA. Both MPAs provide protection for unique deep-sea habitat.

There are also two places along the California coast where submarine canyons come so close to the mainland that scuba divers are able to reach their shallow extensions very near to shore. Divers regularly visit the heads of Carmel Canyon and La Jolla Canyon, both of which are located in state marine reserves (SMRs) and can be accessed from the beach by intermediate to advanced divers. In both locations, unique biological habitats can be seen on the upper canyon rims around 60 to 100 feet below the surface. Off Monastery Beach in Point Lobos SMR divers can witness “sand falls” where beach sand flows into the abyss of the Carmel Canyon, as well as craggy outcroppings where abundant marine life benefits from the nutrient-rich waters transported up from the depths on ocean currents. Beyond the shallow rims of these diver-accessible canyons lie miles and miles of deep canyon walls with rocky outcroppings and dynamic ocean conditions.

To get a glimpse of the vast deep-sea world just off the California coast, which is mostly far too deep for scuba divers, researchers used a remotely operated vehicle known as an ROV. The California Department of Fish and Wildlife (CDFW) partnered with Marine Applied Research and Exploration (MARE), using MARE’s ROV Beagle to survey several of the canyons found in MPAs. The partnership was a part of statewide monitoring efforts that extended from Crescent City in northern California to San Diego in southern California. Researchers recorded video and captured photos from submarine canyons deeper than 2,000 feet, beyond the point where sunlight can penetrate and at temperatures ranging into the low forties (Fahrenheit).

ROV crews studied submarine canyons in the north at Mattole Canyon SMR (Humboldt County), Soquel Canyon SMCA near Santa Cruz (Santa Cruz County), Portuguese Ledge SMCA off Pacific Grove (Monterey County), Big Creek SMR near Big Sur (Monterey County) and Point Dume SMR just west of Malibu (Los Angeles County). Additionally, La Jolla Canyon in Matlahuayl SMR (San Diego County) was visited by MARE’s ROV Beagle in 2010 as part of a separate MPA monitoring study led by researchers at California State University, Monterey Bay.

Benthic siphonophore at Soquel Canyon SMCA (890 feet)

I had the pleasure of joining some of the expeditions, and saw firsthand the challenges these deep habitats posed for the ROV crews. ROV pilots must be skilled at guiding the machines through strong currents and deep depths, and must carefully coordinate each move with the ship’s crew. The ROV’s umbilical cable, which provides electrical power and machine control, hangs from the ship’s winch spool down to the ROV and requires constant attention to keep it from tangling in the craggy, steep canyon walls. The cable resembles a heavy-gauge extension cord, and contains copper wire and fiber optics wrapped in a tough plastic sheath. Deep-sea imagery is live-streamed to the surface via the umbilical cable, which allows the pilot to control the ROV’s maneuvering thrusters and monitor the digital data being collected. More than once, pilots have had to untangle a snagged umbilical cable using highly skilled maneuvers to save the dive and avoid expensive equipment damage, or to avoid losing the half-million-dollar ROV itself.

Piloting an ROV is much like flying a drone or playing a video game, but with very few visual cues. Years of experience have given MARE’s pilots the experience and confidence to operate ROVs in these tough circumstances. Just getting an ROV to the bottom can take as long as 30 minutes, and often longer in swift currents.

Brown cat shark at Big Creek SMR (980 feet)

Because of the depths involved, these ROV dives demanded extraordinarily careful planning. Despite the occasional tense moments while piloting the ROV from the research vessel, we weren’t disappointed by what we found along the canyon walls. From a school of thousands of bright-eyed brown cat sharks at Big Creek SMR, to the otherworldly benthic siphonophore that was found adhered to canyon walls by sticky tendrils, we never knew what mysterious creatures to expect next.

One of the objectives of California’s MPA network is to protect unique habitats like deep sea submarine canyons. Through the lens of an ROV, researchers are able to document, study, and better protect deep water species that are rarely seen unless they are caught by a fishing net or line. These challenging and sometimes risky ROV research expeditions have expanded our understanding of hard-to-visit habitats, and provided a basis for ongoing and future study of these amazing places.

Enjoy a glimpse of the deep in these videos from ROV submarine canyon dives in five of California’s MPAs: Mattole Canyon SMR, Soquel Canyon SMCA, Portuguese Ledge SMCA, Big Creek SMR, and Point Dume SMR.

For more stories, videos, and photos from ROV-based research, enjoy these Marine Management News articles:

Visit CDFW’s Marine Protected Areas web page for more ROV and scuba videos shot in a variety of habitats.

Editor’s note: This article was updated in September, 2022.

logo post by Mike Prall, CDFW Environmental Scientist

Learn more about MPAs by diving into the
Exploring California’s Marine Protected Areas series!